New and powerful tools have been developed to address each of them in
the last several years, e.g., the Saak [1]} and Saab
transforms [2]} for Problem 1, the PixelHop
[3]}, PixelHop++ [4]} and
IPHop [5]} learning systems for Problem 2, the
discriminant and relevant feature tests [6]} for
Problem 3, the subspace learning machine [7]} for
Problem 4. The original ideas scattered around in different papers.
They will be systematically introduced here.
